Recently, in accordance with development of downsized mobile electronic devices, portable personal computers are widely used, and portable small products are increased as peripheral devices for such personal computers. Generally, as mobile devices use a battery as a driving power source, a function of notifying a user of a battery residual capacity is indispensable.
As battery residual capacity (residual electric capacity in a battery) detection methods, the following two methods are known.
One method is an energy integration method of integrating discharged electric current and subtracting the integrated current value from a total capacity of a battery. This method has an advantage that the residual capacity can be calculated with high accuracy, but has a disadvantage that, as a system realizing the method is complicated, this results in a relatively high cost.
The other method is a voltage detection method of estimating a residual capacity from a battery voltage. Since it is difficult to estimate a residual capacity from a battery voltage, this method has a disadvantage that the accuracy of battery residual capacity detection is low, but the method has an advantage that, as a system realizing the method is simple, it can be realized at a low cost.
The present invention relates to the method of detecting a battery residual capacity by using the voltage detection method.
In a case where a battery residual capacity is detected by utilizing the voltage detection method, as a proper voltage cannot be detected when the battery is under no load, it is necessary to apply a predetermined load to the battery. However, in electronic devices having an actuator such as a stepping motor, the load is often unstable depending on the driving status. On the other hand, even in one battery, as an output voltage varies depending on load, it is necessary to create a status under a predetermined load for battery residual capacity detection.
For this purpose, conventionally, voltage detection is performed in a status where the battery is under a predetermined load while the motor held in a stopped state is intentionally excited. The intentional excitation of a motor held in a stopped state for battery voltage detection will be referred to as “dummy excitation”.
In a portable inkjet printing apparatus, when a battery voltage is lowered and a necessary battery residual capacity for normal operation of the apparatus cannot be ensured, it is necessary to perform processing including discharging of a printing medium such as a print sheet from the apparatus main body and capping of a printhead for preventing the ink discharge surface of the printhead from drying and the like before the power is turned off.
Further, in a case where it is determined as a result of battery residual capacity detection of the printing apparatus that the battery does not have a sufficient residual capacity for the above power-off processing, the operation of the apparatus is stopped before completion of the processing. Since this may damage the printhead, such inconvenience must be most carefully avoided when the battery residual capacity becomes small in a portable inkjet printing apparatus. As a precautional measure against such trouble, it may be arranged such that dummy excitation and battery voltage detection are frequently performed when the apparatus is driven with a battery.
However, dummy excitation cannot be always performed. Especially, in an electronic apparatus having plural motors such as an inkjet printing apparatus, dummy excitation must be performed when all the motors are stopped or a battery is under a predetermined load. Accordingly, the operation of battery residual capacity detection is periodically performed in a battery-driving printing operation sequence.
Generally, a printing apparatus operates through a predetermined sequence from power-on, printing, to power-off to a certain degree. In other words, as a next operation including a user's print instruction can be predicted to a certain degree, the operation of battery voltage detection by dummy excitation is set at an arbitrary timing in the apparatus operation sequence, thereby battery voltage can be detected by a predetermined time.
In this operation sequence of a printing apparatus, it is also necessary to detect a battery voltage during printing using a printhead. For example, upon printing character patterns such as text, printing time is not so long and the battery residual capacity causes no problem; however, upon printing a photograph, a figure or the like, it takes a comparatively long time by the completion of printing. In such case, there is a possibility that the battery residual capacity is reduced during the printing and termination processing cannot be normally performed. For this reason, it is necessary to perform battery voltage detection during printing.
Further, Japanese Patent Application Laid Open Nos. 7-32703, 7-132650 and 10-336400 propose control for suppression of battery consumption by lowering a printing speed and/or printing quality when a battery residual capacity becomes small.
However, since dummy excitation during printing takes time, the printing speed is extremely lowered.
On the other hand, one of the significant capabilities of a printing apparatus is printing speed. Particularly, a printing speed when printing is continuously performed on plural print sheets (continuous printing) is represented as throughput (in ppm (pages per minute), i.e., the number of print sheets per minute). This is an indicator of printing speed of the printing apparatus.
Accordingly, it is necessary to detect a battery voltage during printing, and it is necessary to avoid reduction of printing speed due to dummy excitation for the battery voltage detection.